For many years, haul rope-based transportation systems have been extensively used. Thus, ski lifts, chair lifts and aerial tramways have long employed a metal haul rope or cable to act as a traction element for a vehicle, which can take the form of a chair, gondola or tramway cabin. More recently, haul rope technology has been adapted to automated people mover systems, as for example is shown and described in my U.S. Pat. No. 5,406,891. Such systems employ a passive or unpowered vehicle which is supported by tires or sheaves on a guide track and propelled along the track over a transit path in either a loop or shuttle, by a haul rope. The haul rope is driven by bull wheels at end of the path and/or intermediate rope engaging drive wheels.
Haul rope-based people mover systems have numerous advantages, but they also pose certain problems, particularly in loop or curved track applications. Guiding of the haul rope under relatively high tension forces has attendant cost disadvantages, and driving of the haul rope intermediate ends of transit path is relatively difficult.
More recently, I have developed an automated people mover system which employs a flexible traction belt, instead of a haul rope. The use of a traction belt greatly simplifies the problems associated with driving the vehicle in a loop or along a curved track. Unlike haul ropes, a traction belt can be easily driven from locations intermediate the ends of the belt. Thus, a distributed drive system can be employed with a traction belt-based system, rather than drive assemblies positioned only at the ends of the transit path. As set forth in my U.S. Pat. No. 5,445,081, a plurality of belt-engaging drive wheels can be distributed along virtually any configuration of transit path so as to frictionally engage and propel the belt, and thus the vehicle.
The use of flexible conveyor-type belting as a tension or traction element in a transportation system also is described in U.S. Pat. No. 3,537,402 to Harkess. In the Harkess patent, the transportation system employs a flexible belt traction member which is not a continuous or endless belt. Instead, the Harkess traction belt extends in front of the vehicle only, with a locomotive coupled to the traction belt to maintain the belt taut so that friction drives distributed around the transit path can pull the vehicle, a loaded belt train. The locomotive constantly exerts a pulling or tension force on the traction belt in front of the vehicle, and the drive wheels in front of the vehicle also apply a tension force to the belt to propel the vehicle. Steering of the Harkess vehicle is accomplished by guide wheels which support the vehicle on the track or support structure.
It is also known in the prior art to drive transportation vehicles using relatively rigid shoes or drive fins that extend substantially over the length of the vehicle. U.S. Pat. No. 4,361,094 to Schwarzkopf, for example discloses such a system. The Schwarzkopf vehicle is guided or steered by rails and a longitudinally incompressible drive member or fin is driven between drive rollers or wheels. Similarly, U.S. Pat. No. 3,880,088 to Grant is typical of a transportation system in which frictional drive wheels are distributed along the track and engage a relatively rigid surface on the vehicle to propel the same.
While transportation systems which engage a fin or shoe over the length of the vehicle are capable of applying compressive loads along the track to both brake and propel the vehicle, these systems are limited as to the length over which both traction (tension) and compression forces may be applied. Moreover, steering or assisting in the steering of the vehicles in such prior art systems using the propulsion assemblies has not been attempted.
More generally, alternate automated people mover systems have included magnetic levitation systems, hover craft systems, and linear motor-based systems. The primary disadvantage of such systems is that of cost. The cost of the vehicle and the cost of the track on which it is transported are substantial. More particularly, the track construction is critical to proper operation of the vehicle. Track tolerances of one to two millimeters are common. This greatly increases construction costs and can pose serious problems in seismic areas or areas in which ground settling is difficult to prevent.
In long-haul transportation systems, the curves are usually relatively gradual and uncomfortable lateral accelerations, as a result of turning, are easily minimized. In people mover applications the transit path is typically shorter and turns typically have tighter radii than in long-haul transit systems, e.g. 40 feet or less. One problem which is common to virtually all automated people mover systems, therefore, is the problem of lateral guiding or steering of the vehicle without uncomfortable lateral accelerations. Most typically people mover steering is accomplished by flanged load-supporting wheels or lateral guide wheels which engage a guiding surface of the support structure. The natural tendency of a set of wheels, or bogey, is to try to maintain the vehicle in a straight path. On turns, therefore, the vehicle wheels tend to fight the turn as they hunt for or oscillate around, a nominal turn path. The attendant lateral accelerations can be unpleasant to riders.
Another problem encountered in turning is that the trackway must be sloped (super elevated) in order to tilt the vehicle into the turn to offset the centrifugal force around the turn and is required by most codes if the centrifugal acceleration is 0.10 g or more. Vehicle tilting gives the riders a comfortable ride around the turn. The cost of building a trackway having tilted turns, which are often compounded by being on a grade, can be very substantial, particularly if all of the dimensions must be held within a few millimeters.
Still a further problem which has been encountered with automated people mover systems of the traction-type is braking. Flexible belts, for example, of the type in my U.S. Pat. No. 5,445,081 and in Harkess U.S. Pat. No. 3,537,402, are well suited for propulsion using friction drives because the belt will withstand substantial tension forces. Braking, however, is another problem because the inherent flexibility of the belt will not withstand compression loading without buckling. Accordingly, the belt must either be braked from behind the vehicle, which is not possible with Harkess because there is no belt behind the vehicle, or auxiliary braking must be provided, for example, by frictional braking against a shoe or surface on the vehicle or by braking of the wheels of the vehicle.
Accordingly, it is an object of the present invention to provide a transportation system suitable for use as a short-haul people mover which has greatly improved propulsion system and steering control and has a greatly reduced cost of construction of the track or support structure.
Another object of the present invention is to provide a transportation system suitable for use as an automated people mover in which the track is active, the vehicle is passive and vehicle steering can be accomplished in part by using the vehicle propulsion system.
Still a further object of the present invention is to provide a vehicle propulsion system for an automated people mover which will allow multiple vehicles to be independently run on the support track while still affording independent braking and acceleration control of each vehicle.
Still another object of the present invention is to provide a transportation system which is durable, relatively low in cost to construct, inexpensive to maintain, adaptable to a wide range of applications, less sensitive to ground settling, and more comfortable for passengers.
The transportation system of the present invention has other objects and features of advantage which will become more apparent from, and are set forth in more detail in, the accompanying drawing and the following description of the Best Mode of Carrying Out the Invention.